SCREENING APPARATUS

Abstract: A mixture of liquid and solid sewage flows in a stream along a channel (2) in the direction from right to left as seen in the Figure. A screening apparatus includes an endless screening belt (4) located with its lower inlet region in the sewage stream. The belt (4) consists of pivotally connected screening elements (12) made of perforated plate. Each screening element (12) consists of a shorter part (14) and a longer part (16) connected at an acute angle to one another. In operation, the belt (4) travels anti-clockwise causing solid sewage greater than the size of the perforations to be carried upwardly on the shorter parts (14). The liquid sewage effluent drains from the screening elements (12) as they ascend. When each screening element (12) reaches the upper region of the belt (4) the screening element tilts in a clockwise direction to release the solid sewage which drops to a screw conveyor (30) which conveys the solid sewage to a desired location. The upper region (22) of the belt (4) extends upstream of the inlet region of the belt (4) so that any solid sewage spilt from the upper region of the belt (4) which is not collected by the screw conveyor (30) falls back into the channel (2) upstream of the inlet region of the belt (4). This arrangement reduces the risk of solid sewage entering and polluting the cleansed liquid sewage effluent downstream of the conveyor belt (4).

Description: SCREENING APPARATUS The present invention relates to apparatus for removing solid materials from a liquid. The invention is particularly concerned with but not restricted to an apparatus for removing solid sewage from a mixture of liquid and solid sewage during the purification of sewage. In a previously proposed sewage purification system the mixture of liquid and solid sewage travels along an open- topped channel to a conveyor screen arranged to lift the solid sewage out of the channel. This conveyor screen is in the form of an endless belt travelling between a lower region located in the channel and an upper region located above the channel. The direction of flow of the liquid and solid mixture along the channel, and the direction of travel of the conveyor screen belt are such that the ascending part of the conveyor screen belt may be inclined in the downstream direction for at least part of its travel between the upper and lower regions. The conveyor screen belt is arranged so that when solid sewage arrives at the upper region of the belt, the sewage falls off the belt and is collected in a transporter, such as a screw- conveyor, and transported to a required location. A disadvantage of the known arrangement is that if any of the solid sewage falling off the conveyor screen belt should miss the transporter then this sewage will fall into the channel downstream of the conveyor screen belt thereby polluting the cleaner liquid effluent downstream of the conveyor. It is an aim of the invention to alleviate this disadvantage, and according to one aspect of the present invention there is provided apparatus for removing solid material from a liquid stream; said apparatus comprising screening means having an inlet region located in the stream to extract therefrom said solid material in a preselected size range, said screening means being operable to convey said extracted solid material to an outlet region, transporting means to receive solid material released from said outlet region and transport said solid material to a required location, in which the outlet region is located above and upstream of said inlet region whereby extracted solid material not collected by the transporting means returns to the stream upstream of the inlet region of the screening means. The screening means may be in the form of an endless belt, and in a preferred embodiment of the invention this belt may comprise a plurality of pivotally connected screening elements which are arranged longitudinally with respect to one another. Each screening element may be of sheet form and comprise two connected generally planar sections which are located at an angle to one another. Each screening element may be perforated, or made of woven or spaced elements and the apertures will be dimensioned to allow passage therethrough of solid material below said preselected size range, and liquid. The apparatus may include a chain connected to the screening means for movement therewith, and driving means for driving the chain. The links of the chain may be connected to associated pivotal connections of the screening elements. According to another aspect of the present invention there is provided a method of removing solid material from a liquid stream; said method comprising collecting said solid material on the inlet region of a conveyor screen located in the stream, conveying said collected material to an outlet region of the conveyor screen for transfer to a transporting means in which the collected solid material is conveyed upwardly and in an upstream direction with respect to the conveyor screen inlet region whereby solid material accidentially or prematurely released from the conveyor screen outlet region reenters the stream upstream of the conveyor inlet region. One embodiment of the invention will now be described by way of example with reference to the accompanying illustrative diagrammatic drawings in which:- Figure 1 is a side elevation of a screening apparatus for removing solid sewage from a liquid-solid sewage mixture, Figure 2 is a front view of the screening apparatus of Figure 1 as viewed from the upstream direction, Figure 3 is a view of screening elements of the screening apparatus, perpendicular to the conveyor screen, Figure 4 is a side elevation of two adjacent screening elements of the screening apparatus. Figure 5 is a view of the chain drive of the screening apparatus perpendicular to the conveyor screen. Referring to the drawings, a mixture of liquid and solid sewage flows in a stream along a channel 2 in the direction from right to left as seen in Figure 1. An endless screening conveyor belt 4 is located with its lower inlet region immersed in the sewage stream, and the belt 4 is driven by a driving wheel 6 located at the upper outlet region of the belt. The driving wheel 6 is mounted on a shaft 7 and driven from a drive motor 8 by means of a drive belt or chain 10. The screening conveyor belt 4 is made up of a plurality of screening elements 12 which are pivotally connected and arranged longitudinally as shown particularly in Figure 1. Referring particularly to Figures 1 and 4, each screening element is of generally plate form and consists of a shorter part 14 and longer part 16 connected at an acute angle to one another. Each screening element 12 has transversely extending tubular hinge members extending across part of its opposite ends. As shown in Figure 3, the left hand screening element 12 has two hinge members 18 extending along the outer portions of its left hand end and a single hinge member 20 extending along the central portion of its right hand end. The right hand screening element 12 has a similar arrangement of hinge members 18 and 20, and it will be seen that the two outer hinge members 18 of the right hand screening element 12 are located coaxially with the central hinge member 20 of the left hand screening element 12 to receive a single hinge rod 32 thereby completing the hinge connection of the two screening elements 12. It will be understood that all the screening elements 12 of the screening conveyor belt 4 are connected in this way. Each screening element is perforated with apertures of typically 6mm diameter, or apertures having a size appropriate to the application, thereby enabling the screening elements 12 to extract from the liquid stream and convey to the upper region of the conveyor belt 4 solid sewage having a minimum dimension greater than the hole or aperture size chosen. Referring to Figures 1, 4 and 5 flanged rollers 34 are mounted on each end of each hinge rod 32. The conveyor belt 4 is drawn by two endless chains 36 which are located one on each side of the belt 4. Referring to Figure 5 the chains are similar to a bicycle chain and have alternate inner links 38 and outer links 40 which are mounted on the hinge rods 32. These chains 36 are engaged by circumferential teeth on driving chain wheels mounted on the shaft 7 to drive the conveyor belt 4. At the lower part of the belt 4 these chains 36 are engaged by a circular guide rail 42. In order to maintain the required configuration of the conveyor belt 4, the rollers 34 run on guide rails 44 secured to the main frame 46 of the apparatus. Referring to Figure 5 each screening element 12 may have upstanding side plates 48 at both sides to prevent solid sewage from falling off the sides of the conveyor belt 4. Referring particularly to Figure l, the screening conveyor belt 4 is driven in an anti-clockwise direction, and the belt 4 extends upwardly from the channel 2 with the upper region 22 of the belt 4 inclined upstream with respect to the inlet region of the belt. A rotatable cleaning brush 24 is driven from a drive motor 26 by a drive belt 28 to clean each screening element 12 in sequence as it passes round the driving wheel 6. When the screening elements 12 are travelling between the inlet and outlet regions of the conveyor belt 4 the shorter part 14 and the longer part 16 of adjacent screening elements 12 are located at an angle A (Fig 4) . As the screening elements pass round the driving wheel 6 in the region of the cleaning brush 24, the shorter and longer parts 14 and 16 of adjacent screening elements 12 open out so that they are connected at a larger angle B thereby facilitating the cleaning operation by the rotating cleaning brush 24, and reducing the risk of solid sewage adhering to the screening elements 12. A deluge device (not shown) sprays cleaning liquid onto the screening elements 12 in the region of the cleaning brush 24 thereby assisting the cleaning operation of the brush 24. The face of each screening element 12 is smooth with no projections, thereby preventing solid sewage material from being retained on the screening elements, and generally assisting the brushing and washing operation. By having elements of this general shape it is possible to increase the perforated open area of the elements and thereby increase the flow through the screen. In operation, the stream of liquid and solid sewage travels from right to left along the channel 2, and the conveyor belt 4 is driven in an anti-clockwise direction as shown in Figure 1. The inlet region of the conveyor belt 4 is located in the sewage stream and extracts therefrom solid sewage having a minimum dimension greater than the aperture size. This solid sewage is carried on the shorter part 14 of each screening element 12, and the liquid sewage effluent drains from the screening element as it ascends the right-hand part of the conveyor belt as shown in Figure 1 towards the upper region 22 of the belt. When each screening element 12 reaches this upper region of the belt 4 the screening element tilts in a clockwise direction thereby releasing the solid sewage which drops into a screw conveyor 30 which conveys the solid sewage to a desired location for removal. It will be appreciated particularly from Figure l that the screening conveyor belt 4 extends upwardly in a generally vertical direction from the channel 2 and that the upper region 22 of the belt 4 extends above the channel 2 and upstream of the inlet region of the conveyor belt 4. The channel 2, the conveyor belt 4 and the screw conveyor 30 are arranged so that any solid sewage spilt from the upper region of the belt 4 which is not collected by the screw conveyor 30 falls back into the channel 2. Because the upper region 22 of the conveyor belt 4 extends in a direction upstream of the inlet region of the belt 4, this solid sewage material which is not collected by the screw conveyor 30 re-enters the channel 2 upstream of the conveyor belt inlet region and is consequently again extracted from the liquid-solid sewage stream when it reaches the inlet region of the conveyor belt 4. This arrangement has the very important advantage that it reduces the risk of solid sewage material entering and polluting the at least partially cleansed liquid sewage effluent downstream of the conveyor belt 4. The moving parts of the described apparatus will normally be totally closed by suitable guard members, and obstruction to flow in the channel 2 will be kept to an absolute minimum. It is to be understood that the conveyor belt 4 does not have to travel in an anticlockwise direction, and the belt 4 does not have to extend vertically from the channel 2. The important feature of the invention is that once removed from the sewage stream the solids are 8 not re introduced in any way into the downstream screened flow. The screening elements 12 have a large open area produced by the apertures thereby keeping the head loss to a minimum. As described on page 6 as the screening elements pass round the driving wheels 6 these screening elements open out thereby facilitating the cleaning operation. The guide rails 44 for supporting the belt 4 are designed to reduce the load on the belt and driving mechanism to a minimum thereby reducing wear and increasing the serviceable life of the apparatus.

Claims: CLAIMS 1. Apparatus for removing solid material from a liquid stream; said apparatus comprising screening means having an inlet region located in the stream to extract therefrom said solid material in a preselected size range, said screening means being operable to convey said extracted solid material to an outlet region, transporting means (30) to receive solid material released from said outlet region and transport this solid material to a required location, in which the outlet region is located above and upstream of said inlet region whereby extracted solid material not collected by the transporting means returns to the stream upstream of the inlet region of the screening means. 2. Apparatus as claimed in claim 1 in which the screening means comprises an endless belt (4). 3. Apparatus as claimed in claim 2 in which the screening means comprises a plurality of pivotally connected screening elements (12) which are arranged longitudinally to one another. 4. Apparatus as claimed in claim 3 in which each screening element comprises two connected generally planar sections (14) and (16) which are located at an angle to one another. 5. Apparatus as claimed in claim 3 or claim 4 in which each screening element (12) is of sheet form with apertures therein. 6. Apparatus as claimed in claim 3 or claim 4 in which each screening element is made of woven or spaced elements. 7. Apparatus as claimed in any one of claims 3 to 6 including a chain (36) connected to the screening means (4) for movement therewith, and driving means (6) for driving the chain. 8. Apparatus as claimed in claim 7 in which links (38,40) of the chain are connected to associated pivotal connections (32) of the screening elements (12). 9. Apparatus as claimed in any preceding claim including guide means (44) to maintain the required configuration of the screening means (4). 10. Apparatus as claimed in claim 9 including rollers (34) on the screening means (4) arranged to run on the guide means (44) . 11. A method of removing solid material from a liquid stream; said method comprising collecting said solid material on the inlet region of a conveyor screen located in the stream, conveying said collected material to an outlet region of the conveyor screen for transfer to a transporting means in which the collected solid material is conveyed upwardly and in an upstream direction with respect to the conveyor screen inlet region whereby solid material accidentially or prematurely released from the conveyor screen outlet region re-enters the stream upstream of the conveyor screen inlet region. 12. Apparatus for removing solid material from a liquid stream substantially as herein described and shown in the accompanying drawings. 13 A method of removing solid material from a liquid stream substantially as herein described w i th reference to the accompanying drawings.

Inventors: MILES ALAN ALFRED, MILES, ALAN, ALFRED
Applicants: MILES ALAN ALFRED, VICKERYS LTD, MILES, ALAN, ALFRED, VICKERYS LIMITED
Application year: 1994
Main classification: B07B1
IPC codes: B07B1, E02B8